There are military and other applications in which it is desirable to be able to detect one or more moving projectiles. Systems have previously been developed to detect one or more large projectiles, such as an artillery shell. However, it is more difficult to detect smaller projectiles, such as a sniper's bullet. Although existing systems have been generally adequate for their intended purposes, they have not been satisfactory in all respects, and none of them have proved to be suitably accurate and efficient at detecting just a single shot from a sniper rifle. Further, some of these systems routinely generate false alarms in response to irrelevant flashes and/or reflections, while others routinely generate false alarms in response to irrelevant acoustic effects. Still others are highly directional, which is problematic in situations where it is difficult to identify the particular direction from which hostile fire is coming.